[clang] Effect analysis: correctly detect `(x ? a : b)` as nonblocking when a and b are (PR #111224)

[Chris Apple via cfe-commits]

https://github.com/cjappl approved this pull request.

LGTM. 

Will let a little time pass to let Sirraide chime in, because this section of the code isn't my forte. If you want this merged ASAP @dougsonos and you feel confident in it, ping me and I can merge.

https://github.com/llvm/llvm-project/pull/111224